Methods for forming recesses in source/drain regions and devices formed thereof

ABSTRACT

Embodiments disclosed herein relate generally to methods for forming recesses in epitaxial source/drain regions for forming conductive features. In some embodiments, the recesses are formed in a two-step etching process including an anisotropic etch to form a vertical opening and an isotropic etch to expand an end portion of the vertical opening laterally and vertically. The recesses can have increased contact area between the source/drain region and the conductive feature, and can enable reduced resistance therebetween.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. application Ser. No.15/992,598, filed on May 30, 2018, entitled “Methods for FormingRecesses in Source/Drain Regions and Devices Formed Thereof” which ishereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. When a semiconductor device such as a finfield-effect transistor (FinFET) is scaled down through varioustechnology nodes, several strategies have been employed to improvedevice performance, such as using high-k dielectric materials and metalgate electrode structures.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 and 2A-2B, 3A-3B, 4A-4B, 5A-5B, 6A-6B, and 7A-7B are schematicthree-dimensional and cross-sectional views of a portion of asemiconductor device corresponding to various stages in an examplemanufacturing process according to some embodiments.

FIGS. 8A-8B and 9A-9B are schematic cross-sectional views of a portionof a semiconductor device corresponding to various stages in anotherexample manufacturing process according to some embodiments.

FIG. 10 illustrates a portion of the cross-sectional view of FIG. 5A tofurther illustrate additional details in accordance with someembodiments.

FIG. 11 illustrates a portion of the cross-sectional view of FIG. 6A tofurther illustrate additional details in accordance with someembodiments.

FIG. 12 illustrates a portion of the cross-sectional view of FIG. 7A tofurther illustrate additional details in accordance with someembodiments.

FIG. 13 illustrates a portion of the cross-sectional view of FIG. 8A tofurther illustrate additional details in accordance with someembodiments.

FIG. 14 illustrates a portion of the cross-sectional view of FIG. 9A tofurther illustrate additional details in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments disclosed herein relate generally to methods for formingrecesses in epitaxial source/drain regions for forming conductivefeatures. In some embodiments, the recesses are formed in a two-stepetching process including an anisotropic etch and an isotropic etch. Therecesses can have increased contact area between the source/drain regionand the conductive feature, and can enable reduced resistancetherebetween.

The foregoing broadly outlines some aspects of embodiments described inthis disclosure. It is contemplated that the concepts of the presentdisclosure may be implemented for a planar transistor device or for athree-dimensional transistor device, such as the semiconductor device240 described in this disclosure. Some example devices for which aspectsdescribed herein may be implemented include fin field effect transistors(FinFETs), Horizontal Gate All Around (HGAA) FETs, Vertical Gate AllAround (VGAA) FETs, nanowire channel FETs, strained-semiconductordevices, silicon-on-insulator (SOI) devices, or other devices.

FIG. 1 illustrates an example of the semiconductor device 240 in athree-dimensional view. FIGS. 2A-2B through 7A-7B and 8A-8B through9A-9B are schematic cross-sectional views of a portion of thesemiconductor device 240 corresponding to various stages of fabricationaccording to some embodiments. It is noted that the methods describedherein may be utilized to form any other semiconductor structures notpresented herein. Those having ordinary skill in the art shouldrecognize that the full process for forming a semiconductor device andthe associated structures are not illustrated in the drawings ordescribed herein. Although various operations are illustrated in thedrawings and described herein, no limitation regarding the order of suchsteps or the presence or absence of intervening steps is implied.Operations depicted or described as sequential are, unless explicitlyspecified, merely done so for purposes of explanation without precludingthe possibility that the respective steps are actually performed inconcurrent or overlapping manner, at least partially if not entirely.

As shown in FIG. 1, the semiconductor device 240 has a fin 274 formed ona semiconductor substrate 270. The semiconductor substrate 270 may be orinclude a bulk semiconductor substrate, a semiconductor-on-insulator(SOI) substrate, or the like, which may be doped (e.g., with a p-type oran n-type dopant) or undoped. In some embodiments, the semiconductormaterial of the semiconductor substrate 270 may include an elementalsemiconductor including silicon (Si) or germanium (Ge); a compoundsemiconductor; an alloy semiconductor; or a combination thereof.

Each fin 274 provides an active area where one or more devices areformed. The fin 274 is fabricated using suitable processes includingmasking, photolithography, and/or etch processes to form trenches 253 inthe substrate 270, leaving the fin 274 extended upwardly from thesubstrate 270. The trenches 253 may then be filled with an insulatingmaterial such as an oxide (e.g., silicon oxide), a nitride, the like, ora combination thereof. The insulating material may be recessed, such asby using an acceptable etch process, to form the isolation regions 278.The insulating material is recessed such that the fin 274 protrudesabove and from between neighboring isolation regions 278.

The semiconductor device 240 includes gate structures 251 formed overtop surfaces and along sidewalls of the fin 274. The gate structures 251extend longitudinally perpendicularly to the fin 274. Each gatestructure 251 includes a gate dielectric 280, a gate layer 282 over thegate dielectric 280, and a mask 284 over the gate layers 282. Thesemiconductor device 240 also includes source/drain regions 292 disposedin opposing regions of the fin 274 with respect to the gate structures251.

The gate structures 251 can be operational gate stacks in a gate-firstprocess or can be dummy gate stacks in a replacement gate process. Forsimplicity, a replacement gate process is described herein; a personhaving ordinary skill in the art will readily understand modificationsto processing described herein to implement a gate-first process. In areplacement gate process, the gate dielectric 280 may be an interfacialdielectric, and the gate layer 282 may be a dummy gate. The gatedielectrics 280, the gate layers 282, and the mask 284 for the gatestructures 251 may be formed by sequentially forming respective layers,such as by appropriate deposition techniques, and then patterning thoselayers into the gate structures 251, such as by appropriatephotolithography and etching processes. The interfacial dielectrics mayinclude or be silicon oxide, silicon nitride, the like, or multilayersthereof. The dummy gates may include or be silicon (e.g., polysilicon)or another material. The masks may include or be silicon nitride,silicon oxynitride, silicon carbon nitride, the like, or a combinationthereof.

FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section A-A is in a plane along, e.g., channels inthe fin 274 between opposing source/drain regions 292. Cross-section B-Bis in a plane perpendicular to cross-section A-A and is across asource/drain region 292 in the fin 274. Subsequent figures refer tothese reference cross-sections for clarity. The following figures endingwith an “A” designation illustrate cross-sectional views at variousinstances of processing corresponding to cross-section A-A, and thefollowing figures ending with a “B” designation illustrate cross-sectionviews at various instances of processing corresponding to cross-sectionB-B. FIGS. 2A and 2B illustrate in the respective cross-sectional viewsthe semiconductor device 240 depicted in the three-dimensional view ofFIG. 1.

In FIGS. 3A and 3B, gate spacers 286 are formed along sidewalls of thegate structures 251 (e.g., sidewalls of the gate dielectrics 280, gatelayers 282, and masks 284) and over the fin 274. The gate spacers 286may be formed by conformally depositing one or more layers for the gatespacers 286 and anisotropically etching the one or more layers, forexample. The one or more layers for the gate spacers 286 may include amaterial different from the material(s) for the gate structure 251. Insome embodiments, the gate spacers 286 may include or be a dielectricmaterial, such as silicon oxygen carbide, silicon nitride, siliconoxynitride, silicon carbon nitride, the like, multi-layers thereof.

After the gate spacers 286 are formed, source/drain regions 292 may beformed in the fin 274, as depicted in FIGS. 3A and 3B. In some examples,such as illustrated in the figures, recesses can be etched in the fin274 using the gate structures 251 as masks (such that recesses areformed on opposing sides of the gate structures 251), and a material maybe epitaxially grown in the recesses to form the source/drain regions292. Additionally or alternatively, the source/drain regions 292 may beformed by implanting dopants into the fins 274 and/or the epitaxialsource/drain regions 292 using the gate structures 251 as masks (suchthat the source/drain regions are formed on opposing sides of the gatestructures 251).

Depending on the conductivity type of the transistor, the material forthe source/drain regions 292 may be chosen to include or be silicongermanium, silicon carbide, silicon phosphorus, silicon carbonphosphorus, germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. In some examples, SiGe may be included inthe source/drain regions 292 for p-type devices, while SiCP or SiP maybe included in the source/drain regions 292 for n-type devices. Asillustrated in FIG. 3B, due to blocking by the isolation regions 278,the material in the source/drain regions 292 is first grown verticallyin recesses, during which time the source/drain regions 292 do not growhorizontally. After the recesses are fully filled, the material for thesource/drain regions 292 may grow both vertically and horizontally toform facets, which may correspond to crystalline planes of thesemiconductor substrate 270. In some examples, different materials areused for epitaxy source/drain regions for p-type devices and n-typedevices. Appropriate masking during the recessing or epitaxial growthmay permit different materials to be used in different devices.

As shown in FIG. 3A, the epitaxial source/drain regions 292 are formedbetween the gate structures 251 in place of the removed portions of thefin 274. In some embodiments, a cross-sectional area of the epitaxialsource/drain regions 292 along the A-A line may be shaped like ahexagon, although other cross-sectional areas may be implemented, suchas other shapes due to the etching process used to recess the fin 274.The cross-sectional area along the A-A line may have a height 292 h anda width 292 w. In some embodiments, the height 292 h may be in a rangefrom about 40 nm to about 50 nm. In some embodiments, the width 292 wmay be greater than 30 nm, for example, in a range from about 30 nm toabout 50 nm.

In FIG. 3B, the epitaxial source/drain regions 292 are grown epitaxiallyfrom the fin 274 along a recess between the isolation regions 278. Theepitaxial source/drain region 292 extends upward from the recess betweenthe isolation regions 278 forming a substantially rhombus shape alongthe B-B line due to the crystallographic orientation of the materialbeing grown, although other shapes may be formed. In some embodiments,the epitaxial source/drain regions 292 may have a rhombuscross-sectional area having a top angle 292Q along the B-B line. In someembodiments, the top angle 292Q is in a range from about 60 degrees toabout 160 degrees, for example from about 70 degrees to about 80degrees.

In the example shown in FIGS. 3A and 3B, the epitaxial source/drainregions 292 have varying widths along the respective cross-sections asthe epitaxial source/drain regions 292 are traversed from respectivebottom portions to top portions of the epitaxial source/drain regions292. The width increases from the top portion of the respectiveepitaxial source/drain region 292 to an intermediate portion of theepitaxial source/drain region 292, and then decreases from theintermediate portion of the epitaxial source/drain region 292 to thebottom portion of the epitaxial source/drain region 292.

In FIGS. 4A and 4B, after formation of the source/drain region 292, ancontact etch stop layer (CESL) 296 is conformally formed on surfaces ofthe source/drain regions 292, sidewalls and top surfaces of the gatespacers 286, top surfaces of the masks 284, and top surfaces of theisolation regions 278. A first interlayer dielectric (ILD) 297 is formedon the CESL 296. The CESL 296 and first ILD 297 can be deposited usingany suitable deposition technique. The CESL 296 may include or besilicon nitride, silicon carbon nitride, silicon carbon oxide, carbonnitride, the like, or a combination thereof. The first ILD 297 mayinclude or be silicon dioxide, a low-k dielectric material (e.g., amaterial having a dielectric constant lower than silicon dioxide),silicon oxynitride, phosphosilicate glass (PSG), borosilicate glass(BSG), borophosphosilicate glass (BPSG), undoped silicate glass (USG),fluorosilicate glass (FSG), organosilicate glass (OSG), SiO_(x)C_(y),Spin-On-Glass, Spin-On-Polymers, silicon carbon material, a compoundthereof. A chemical mechanical polishing (CMP) process may then beperformed to planarize the first ILD 297 and the CESL 296 and to removethe masks 284 of the gate structures 251, thereby leveling the topsurface of the first ILD 297 and CESL 296 with the top surfaces of thegate layers 282.

After the CMP process, the gate structures 251 are removed using one ormore etch processes so that replacement gate structures 228 a, 228 b canbe formed in the recesses formed by removing the gate structures 251.Upon removal of the gate structures 251, recesses are formed between thegate spacers 286 where the gate structures 251 are removed, and channelregions of the fins 274 are exposed through the recesses. Thereplacement gate structures 228 a, 228 b are then formed in the recesseswhere the gate structures 251 were removed.

The replacement gate structures 228 a, 228 b each may include, asillustrated in FIG. 4A, an interfacial dielectric 220, a gate dielectriclayer 222, one or more optional conformal layers 224, and a gate metalfill 226. The interfacial dielectric 220 is formed on a top surface andsidewalls of the fin 274 along the channel regions. The interfacialdielectric 220 can be an oxide (e.g., silicon oxide), nitride (e.g.,silicon nitride), and/or another dielectric layer using any suitabledeposition technique.

The gate dielectric layer 222 can be conformally deposited in therecesses where gate stacks were removed (e.g., on the interfacialdielectric 220 and sidewalls of the gate spacers 286) and on the topsurfaces of the first ILD 297, the CESL 296, and gate spacers 286. Thegate dielectric layer 222 can be or include silicon oxide, siliconnitride, a high-k dielectric material, multilayers thereof, or otherdielectric material. A high-k dielectric material may have a k valuegreater than about 7.0, and may include a metal oxide of or a metalsilicate of hafnium (Hf), aluminum (Al), zirconium (Zr), lanthanum (La),magnesium (Mg), barium (Ba), titanium (Ti), lead (Pb), multilayersthereof, or a combination thereof.

The one or more optional conformal layers 224 can include one or morebarrier and/or capping layers and one or more work-function tuninglayers. The one or more barrier and/or capping layers can includetantalum nitride, titanium nitride, the like, or a combination thereof.The one or more work-function tuning layer may include or be aluminumtitanium carbide, aluminum titanium oxide, aluminum titanium nitride,the like, or a combination thereof. The materials for the one or morework-function tuning layer, barrier layer, and/or capping layer areselected so that a desired threshold voltage (Vt) is achieved for thetransistor, which could be a p-type transistor or an n-type transistor.The gate metal fill 226 is formed over the one or more conformal layers224, if implemented, and/or the gate dielectric layer 222. The gatemetal fill 226 can fill remaining recesses where the gate structures 251were removed. The gate metal fill 226 may be or include ametal-containing material such as tungsten, cobalt, aluminum, ruthenium,copper, multi-layers thereof, a combination thereof, or the like.

A planarization process, like a CMP, may remove portions of the layerfor the gate metal fill 226, one or more conformal layers 224, and gatedielectric layer 222 above the top surfaces of the first ILD 297, theCESL 296, and gate spacers 286. The replacement gate structures 228including the gate metal fill 226, one or more conformal layers 224,gate dielectric layer 222, and interfacial dielectric 220 may thereforebe formed.

In FIGS. 5A and 5B, after the planarization process, a second ILD 230 isformed over the replacement gate structures 228, first ILD 297, gatespacers 286, and CESL 296. The second ILD 230 may include or be silicondioxide, a low-k dielectric material, silicon oxynitride, PSG, BSG,BPSG, USG, FSG, OSG, SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers,silicon carbon material, a compound thereof, a composite thereof, thelike, or a combination thereof, and may be deposited using anyacceptable deposition technique.

After the second ILD 230 is formed, source/drain contact openings areformed through the second ILD 230, the first ILD 297, and the CESL 296to the source/drain regions 292 to expose at least portions of thesource/drain regions 292. According to some embodiments, thesource/drain contact openings may be formed through a two-step etchingprocess, which includes an anisotropic etching process to form verticalopenings 232 as shown in FIGS. 5A and 5B and an isotropic etchingprocess to increase surface area at the bottom of the vertical openingas shown in FIGS. 6A and 6B and FIGS. 8A and 8B.

In FIGS. 5A and 5B, vertical openings 232 are formed through the secondILD 230, the first ILD 297, and the CESL 296 using photolithography andone or more anisotropic etch processes. The one or more etch processesmay be a dry etching process, a Deep Reactive-Ion Etching (DRIE)process, or any suitable anisotropic etch process.

FIG. 10 is an enlarged view of region 300 in FIG. 5A showing details ofa bottom portion of the vertical opening 232. The vertical openings 232may be holes or trenches extending into the epitaxial source/drainregions 292. The sidewalls of the source/drain vertical openings 232 aresubstantially vertical, although there may be a small tilt angle. Thevertical opening 232 has a width 232 w near a bottom surface 232 b ofthe vertical opening 232. In some embodiments, the width 232 w may be ina range from about 10 nm to about 40 nm. In some embodiments, the width232 w may be in a range from about 33% to about 100% of the width 292 wof the epitaxial source/drain region 292.

The vertical opening 232 extends into the epitaxial source/drain region292 such that the bottom surface 232 b of the vertical opening 232 isbelow a top 292 t of the epitaxial source/drain region 292. A height 232h indicates a distance from the top 292 t of the epitaxial source/drainregion 292 to the bottom surface 232 b of the vertical opening 232. Insome embodiments, the height 232 h may be in a range from greater than 0nm to about 20 nm. In some embodiments, the height 232 h may be in arange from greater than 0% to about 50% of the height 292 h.

In the example showing FIG. 10, the width of the cross section of thesource/drain region 292 in the A-A cut (or the cross section parallel tothe y-z plane in the x-y-z coordinate shown in FIG. 1) increases fromthe top 292 t to the intermediate portion and decreases from theintermediate portion to a bottom 292 b. A center line 292 c indicatesthe vertical location of the cross-section area with the largest width292 w. Corresponding to the increases and decreases in the width in they-z planes, the size and perimeter of the cross section of thesource/drain region 292 in x-y planes also increase from the top 292 tto the center line 292 c and decreases from the center line 292 c to thebottom 292 b. According to some embodiments, the bottom surface 232 b isabove the center line 292 c.

The vertical opening 232 may be formed by one or more anisotropic etchprocesses. For example, a first anisotropic etch process may beperformed to etch through the second ILD 230, the first ILD 297, and theCESL 296, and a second anisotropic etch process may be performed to forma recess of the height 232 h in the epitaxial source/drain region 292.In some embodiments, the first anisotropic etch process and the secondanisotropic etch process may be the same process performed together in asingle operation. In other embodiments, the first anisotropic etchprocess and the second anisotropic process are different processes withdifferent etch chemistry and/or process parameters.

In some embodiments, the first anisotropic etch process may be a dryetching process, such as a Deep Reactive-Ion Etching (DRIE) process, orany suitable anisotropic etch process. In some examples, the firstanisotropic etch process may be performed using inductive coupled plasma(ICP) or capacitive coupled plasma (CCP) containing oxygen, argon, andone or more fluorocarbon-based gas such as hexafluorobutadiene (C₄F₆),octafluorocyclobutane (C₄F₈), or carbon tetrafluoride (CF₄).

In some embodiments, the second anisotropic etch process may be a dryetch process performed using an inductive coupled plasma (ICP) orcapacitive coupled plasma (CCP) of an etchant. In some embodiments, theetchant may contain one or more fluorocarbon-based gas such as carbontetrafluoride (CF₄), trifluoromethane (CHF₃); one or more fluorine-basedgas, such as nitrogen trifluoride (NF₃), sulfur hexafluoride (SF₆),hexafluorobutadiene (C₄F₆), and octafluorocyclobutane (C₄F₈); achlorine-based gas, such as chlorine gas (Cl₂); and/or a bromine-basedgas such as hydrogen bromide (HBr).

In some examples, the vertical opening 232 is formed by continuouslyperforming a dry etch process using an inductively coupled plasma. TheRF power of the plasma generator can be in a range from about 100 W toabout 2000 W to induce and maintain a plasma of the etchant in a processchamber. The process chamber may have a chamber pressure in a range fromabout 3 mTorr to about 20 mTorr. A bias voltage in a range from about 20volt to about 1500 volt can be applied to the plasma to achieveanistropic etching. In some embodiments, the anisotropic etch processmay be performed for a duration in a range from about 155 seconds toabout 1800 seconds. For example, the etch process may be performed for aduration in a range between about 200 seconds to about 1200 seconds, forexample about 150 seconds, to form an opening through the second ILD230, the first ILD 297, and the CESL 296. After the CESL 296 is removed,an additional etching may be performed for a duration in a range fromabout 5 seconds to about 1050 seconds to recess the vertical opening 232into the epitaxial source/drain regions 292 for the height 232 h.

After formation of the vertical openings 232, the bottom portion of thevertical openings 232 is expanded by an etching process, such as anisotropic etch process. As shown in FIGS. 6A and 6B, expanded openings234 are formed from the vertical openings 232 to allow making electricalcontact to the source/drain regions 292 for the transistors.

In some embodiments, the expanded openings 234 are formed by anisotropic etch process that has a high etching selectivity between theepitaxial source/drain regions 292 to the second ILD 230, first ILD 297,and CESL 296. As a result, the expanded openings 234 and the verticalopenings 232 are substantially the same in dimension in the second ILD230, the first ILD 297, and CESL 296 while the expanded openings 234 aredeeper and have a larger width in the epitaxial source/drain regions 292than the vertical openings 232.

FIG. 11 is an enlarged view of region 302 in FIG. 6A showing details ofa bottom portion of the expanded opening 234. The bottom portion of thevertical opening 232 is shown in dashed line. The expanded opening 234includes a neck portion 234 n formed through the second ILD 23 o, firstILD 297, and CESL 296 and an end portion 234 e formed in the epitaxialsource/drain region 292. The end portion 234 e may have apartial-elliptical cross-section area along the cross-section A-A (referto FIG. 1). The end portion 234 e may have a partial spheroid shape witha partial spheroidal bottom surface 234 cs formed in the epitaxialsource/drain regions 292. As discussed in FIG. 10, the size andperimeter of the cross section of the source/drain region 292 in x-yplanes also increase from the top 292 t to the center line 292 c anddecreases from the center line 292 c to the bottom 292 b. Isotropicallyetching the source/drain region 292 after formation of the verticalopening 232 allows the size of the bottom surface 234 cs to expand, andthus, allows the contact area between the source/drain region 292 andthe metal fill to be filled in the opening 234 to increase.

A height 234 h indicates a distance from the top 292 t of the epitaxialsource/drain region 292 to a bottom point 234 b of the end portion 234 eexpanded opening 234. In some embodiments, the height 234 h may be in arange from about 5 nm to about 20 nm. In some embodiments, the height234 h may be in a range from about 10% to about 50% of the height 292 hof the epitaxial source/drain region 292. In some embodiments, thebottom surface 234 cs is above the position of the center line 292 c ofthe epitaxial source/drain region 292 in the cross-section A-A.

In some embodiments, a width 234 w of the end portion 234 e may be in arange from about 14 nm to about 40 nm. In some embodiments, the width234 w may be in a range from about 30% to about 80% of the width 292 wof the epitaxial source/drain region 292.

The end portion 234 e is formed by laterally expanding the verticalopenings 232 in the epitaxial source/drain region 292 by a lateralexpansion amount dw and by vertically expanding the vertical opening 232in the epitaxial source/drain region 292 by a vertical expansion amountdh. In some embodiments, the vertical expansion amount dh can be in arange from about 5 nm to about 20 nm. For example, for an n-type FinFETdevice, the vertical expansion amount dh can be in a range from about 5nm to about 20 nm. For a p-type FinFET device, the vertical expansionamount dh can be in a range from about 5 nm to about 10 nm. In someembodiments, the lateral expansion amount dw can be in a range fromabout 2 nm to about 10 nm. Hence, the width 234 w of the end portion 234e can be in a range from about 4 nm to about 20 nm greater than thewidth 232 w of the openings 234. In some examples, the width 234 w ofthe end portion 234 e is equal to or greater than about 5% more than thewidth 232 w of the openings 234, such as in a range from about 5% toabout 50% more than the width 232 w of the openings 234. The increasedwidth 234 w can increase surface area to which a conductive feature cancontact the source/drain regions 292. More specifically, for example,for an n-type FinFET device, the lateral expansion amount dw can be in arange from about 2 nm to about 10 nm. For a p-type FinFET device, thelateral expansion amount dw can be in a range from about 2 nm to about 5nm. In some embodiments, the source/drain regions 292 in n-type devicesand in p-type devices can have different dimensions (e.g., widths and/orheights) due to different materials that are epitaxially grown as thesource/drain regions 292. For example, heights and widths ofsource/drain regions 292 of p-type devices can be smaller than heightsand widths of source/drain regions 292 of n-type devices, and hence,vertical expansion amounts dh and lateral expansion amount dw insource/drain regions 292 of p-type devices can be less than verticalexpansion amounts dh and lateral expansion amount dw in source/drainregions 292 of n-type devices.

In some embodiments, the lateral expansion amount dw and the verticalexpansion amount dh may be achieved by an isotropic etch process, suchas an isotropic dry etch process or an isotropic wet etch process.

In some embodiments, the lateral expansion amount dw and the verticalexpansion amount dh may be achieved by a dry etch process using aninductively coupled plasma. The etchant may include one offluorocarbon-based gas such as carbon tetrafluoride (CF₄),trifluoromethane (CHF₃); one or more fluorine-based gas, such asnitrogen trifluoride (NF₃), sulfur hexafluoride (SF₆); a chlorine-basedgas, such as chlorine gas (Cl₂); and/or a bromine-based gas, such ashydrogen bromide (HBr). The RF power of the plasma generator can be in arange from about 100 W to about 2000 W to induce and maintain a plasmaof the etchant in a process chamber. The process chamber may have achamber pressure in a range from about 30 mTorr to about 800 mTorr. Abias voltage in a range from about 0 volt to about 200 volt can beapplied to the plasma. In some embodiments, the dry etch process may beperformed for a duration in a range from about 5 seconds to about 100seconds.

In some embodiments, the isotropic dry etch process may be performed inthe same dry etch chamber where the anisotropic dry etch processes areperformed. Upon formation of the vertical openings 232 shown in FIGS. 5Aand 5B, processing parameters of the dry etch chamber are adjusted toperform an isotropic dry etch to form the end portion 234 e of theexpanded opening 234.

In some embodiments, the lateral expansion amount dw and the verticalexpansion amount dh may be achieved by a wet etch process, for example awet etching process using ammonium hydroxide-peroxide water mixture(APM), such as a wet etching solution having ammonium hydroxide (NH₄OH),hydrogen peroxide (H₂O₂), and deionized water (H₂O) in a ratio betweenabout 1:1:8000 to about 1:1:100 (NH₄OH:H₂O₂:H₂O). In some embodiments,the wet etching process may be performed in an APM mixture for aduration in a range from about 5 seconds to about 300 seconds.

After the formation of the expanded opening 234, a pre-silicide cleanprocess may be performed to remove native oxide (e.g., SiO₂) from thesurfaces of the exposed source/drain regions 292 that may be formed dueto exposure to various etchants during formation of the expandedopenings 234. Example pre-silicide clean processes may include a wetcleaning using a dilute HF aqueous solution or a dry cleaning using aplasma (e.g., a NF₃/NH₃ plasma), or a combination of both. Thechemistries used during the pre-silicide clean may remove native oxideas well as an upper portion of the source/drain regions 292.

A conformal metal layer (not shown) is formed on the surfaces of theexposed source/drain regions 292 (e.g., a partial spheroidal bottomsurface 234 cs) and over the surfaces of the second ILD 230, the firstILD 297, and the CESL 296. In some embodiments, the conformal metallayer may include a single layer of titanium, tantalum, or the like. Inother embodiments, the conformal metal layer may be a multi-layer stack(e.g., a bi-layer), for example a first layer including titanium,tantalum, or the like, and a second layer including titanium nitride,titanium oxide, tantalum nitride, tantalum oxide, or the like. The metallayer may be deposited by atomic layer deposition (ALD), physical vapordeposition (PVD), chemical vapor deposition (CVD), or any suitabledeposition technique.

After formation of the metal layer, a silicide layer 214 is formed onthe source/drain regions 292 by reacting an upper portion of thesource/drain regions 292 with the metal layer, as shown in FIGS. 7A and7B. The substrate 270 is heated, for example, by performing an annealprocess, to cause the silicide reaction to occur wherever the metallayer is in contact with the source/drain regions 292. The annealprocess can be, for example, a rapid thermal anneal (RTA) performed at atemperature in a range from about 400° C. to about 650° C., such asabout 500° C., for a duration in a range from about 10 seconds to about60 seconds. The un-reacted metal layer may be removed by a selectiveetch process that attacks un-reacted metal layer but does not attack thesilicide layer 214, or may remain as an adhesion and/or barrier layer,for example.

As shown in FIGS. 7A and 7B, a barrier layer 219 is conformallydeposited in the expanded openings 234 on the silicide layer 214 andover the second ILD 230, the first ILD 297, and the CESL 296. Thebarrier layer 219 may have a thickness of about 2 nm or less, such about1.8 nm or less, for example about 1.6 nm. The barrier layer 219 may beor include titanium nitride, titanium oxide, tantalum nitride, tantalumoxide, any suitable transition metal nitrides or oxides, the like, orany combination thereof, and may be deposited by ALD, CVD, PECVD,HDP-CVD, low-pressure CVD (LPCVD), or physical vapor deposition (PVD),or any suitable deposition technique. In some examples, the barrierlayer is TiN deposited by ALD.

A conductive material 236 (e.g., contact metal) can be deposited on thebarrier layer 219 and fill the expanded openings 234. The conductivematerial 236 may be or include cobalt, tungsten, copper, ruthenium,aluminum, gold, silver, alloys thereof, the like, or a combinationthereof, and may be deposited by CVD, ALD, PVD, or any suitabledeposition technique. After the conductive material 236 is deposited,excess conductive material 236 and barrier layer 219 may be removed byusing a planarization process, such as a CMP, for example. Theplanarization process may remove excess conductive material 236 andbarrier layer 219 from above a top surface of the second ILD 230, asshown in FIGS. 7A and 7B.

FIG. 12 is an enlarged view of region 303 in FIG. 7A showing the detailsof the conductive material and the silicide layer 214. The silicidelayer 214 corresponds to the partial spheroidal bottom surface 234 cs ofthe end portion 234 e in the expanded opening 234, and therefore, has anincreased surface area. The increased surface area of the silicide layer214 can reduce the resistance between the epitaxial source/drain region292 and the contact formed in the expanded opening 234.

The conductive material 236 includes a neck portion 236 n formed throughthe second ILD 230, first ILD 297, and CESL 296 and an end portion 236 eformed on the epitaxial source/drain region 292. The neck portion 236 nmay be a trench or a cylinder having substantially vertical walls. Theneck portion 236 n may have a width in a range from about 10 nm to about50 nm. The end portion 236 e may have a partial-elliptical cross sectionarea along the cross-section A-A (refer to FIG. 1). The end portion 236e may have a partial spheroid shape with a partial spheroidal bottomsurface facing the silicide layer 214.

A height 236 h of the end portion 236 e may be in a range from about 5nm to about 25 nm. A width 236 w of the end portion 234 e may be in arange from about 15 nm to about 50 nm. In some embodiments, the width236 w of the end portion 236 e may be greater than the width of the neckportion 263 n by an amount in a range from about 2 nm to about 20 nm.The depth and width of the end portion 236 e can enable increasedcontact surface of the end portion 236 e to the epitaxial source/drainregion 292, and thus, can enable reducing resistance therebetween.

The expanded openings may have various shapes depending on, for example,(i) the dimensions of the epitaxial source/drain regions 292, (ii) thedimensions of the vertical openings 232, (iii) whether a passivationprocess is performed prior to the isotropic etch, and/or (iv) theisotropic etch chemistry, each of which may affect the lateral expansionamount dw and the vertical expansion amount dh. For example, the endportion 234 e may be a partial spheroid, such as a partial-sphere,partial-ellipsoid, or the like.

FIGS. 8A and 8B illustrate expanded openings 244 having a differentshape than the expanding openings 234. Similar to the expanded openings234 of FIGS. 6A and 6B, the expanded openings 244 are formed byexpanding the vertical openings 232 of FIGS. 5A and 5B by an isotropicetch process as described with FIG. 6A.

FIG. 13 is an enlarged view of region 304 in FIG. 8A showing details ofthe expanded opening 244. The bottom portion of the vertical opening 232is shown in dashed line. The expanded opening 244 includes a neckportion 244 n formed through the second ILD 230, the first ILD 297, theCESL 296, and the upper portion of the epitaxial source/drain region292, and an end portion 244 e formed in the epitaxial source/drainregion 292 below the top 292 t of the epitaxial source/drain region 292.The neck portion 244 n may be a trench or a cylinder havingsubstantially vertical walls. The neck portion 244 n may have a widththat is substantially similar to the width 232 w of the verticalopenings 232. A bottom 244 nb of the neck portion 244 n is below the top292 t of the epitaxial source/drain region 292.

The end portion 244 e may have an elliptical cross section area alongthe cross-section A-A (refer to FIG. 1). The end portion 244 e may havean ellipsoidal shape with an ellipsoidal surface 244 cs formed in theepitaxial source/drain region 292.

A height 244 h indicates a distance from the top 292 t of the epitaxialsource/drain region 292 to a bottom point 244 b of expanded opening 244.In some embodiments, the height 244 h may be in a range from about 2 nmto about 20 nm. In some embodiments, the height 244 h may be in a rangefrom about 5% to about 50% of the height 292 h of the epitaxialsource/drain region 292. A height 244 eh indicates a height of the endportion 244 e, e.g., a distance from the bottom 244 nb of the neckportion 244 n to the bottom point 244 b of expanded opening 244. Theheight 244 eh is smaller the than height 244 h.

In some embodiments, a width 244 w of the end portion 244 e may be in arange from about 14 nm to about 40 nm. In some embodiments, the width244 w may be in a range from about 10% to about 50% of the width 292 wof the epitaxial source/drain region 292.

The end portion 244 e is formed by laterally expanding the verticalopenings 232 in the epitaxial source/drain region 292 by a lateralexpansion amount dw2 and by vertically expanding the vertical opening232 in the epitaxial source/drain region 292 by a vertical expansionamount dh2. In some embodiments, the vertical expansion amount dh2 canbe in a range from about 2 nm to about 20 nm. For example, for an n-typeFinFET device, the vertical expansion amount dh2 can be in a range fromabout 2 nm to about 20 nm. For a p-type FinFET device, the verticalexpansion amount dh2 can be in a range from about 2 nm to about 10 nm.In some embodiments, the lateral expansion amount dw2 can be in a rangefrom about 2 nm to about 10 nm. Hence, the width 244 w of the endportion 244 e can be in a range from about 4 nm to about 20 nm greaterthan the width 232 w of the openings 244. In some examples, the width244 w of the end portion 244 e is equal to or greater than about 5% morethan the width 232 w of the openings 244, such as in a range from about5% to about 50% more than the width 232 w of the openings 244. Theincreased width 244 w can increase surface area to which a conductivefeature can contact the source/drain regions 292. More specifically, forexample, for an n-type FinFET device, the lateral expansion amount dw2can be in a range from about 2 nm to about 10 nm. For a p-type FinFETdevice, the lateral expansion amount dw2 can be in a range from about 2nm to about 5 nm. In some embodiments, the source/drain regions 292 inn-type devices and in p-type devices can have different dimensions(e.g., widths and/or heights) due to different materials that areepitaxially grown as the source/drain regions 292. For example, heightsand widths of source/drain regions 292 of p-type devices can be smallerthan heights and widths of source/drain regions 292 of n-type devices,and hence, vertical expansion amounts dh2 and lateral expansion amountdw2 in source/drain regions 292 of p-type devices can be less thanvertical expansion amounts dh2 and lateral expansion amount dw2 insource/drain regions 292 of n-type devices.

In some embodiments, one or more of the anisotropic etch processesdescribed above with respect to FIGS. 5A and 5B can passivate surfacesof the vertical openings 232. In some examples, the passivated surfaceshave C_(x)H_(y)F_(z) formed thereon as a result of the anisotropic etchprocess(es). After the anisotropic etch processes of FIGS. 5A and 5B, anadditional anisotropic etch process, such as using a plasma formed fromoxygen (O₂), hydrogen (H₂), or the like, can break through or remove thepassivated surface on the bottom of each vertical opening 232.Subsequently, the isotropic etch can selectively etch through the bottomsurface of the vertical opening 232 (e.g., etch the respective epitaxialsource/drain region 292) without etching the passivated sidewalls of thevertical opening 232 (e.g., including sidewalls of the vertical opening232 in the epitaxial source/drain region 292). Hence, the profile inFIGS. 8A, 8B, and 13 can be achieved.

In FIGS. 9A and 9B, silicide layers 248 are formed on the surfaces ofthe epitaxial source/drain regions 292 in the expanded openings 244; abarrier layer 219 is formed conformally in the expanded openings 244;and a conductive material 246 is formed over the barrier layer 219 andfilling the expanded openings 244, like described with respect to FIGS.7A and 7B.

FIG. 14 is an enlarged view of region 305 in FIG. 9A showing the detailsof the conductive material 246 and the silicide layer 248. The silicidelayer 248 corresponds to the ellipsoidal surface 244 cs of the endportion 244 e in the expanded opening 244 and sidewalls of the epitaxialsource/drain region 292 formed by the neck portion 244 n of the expandedopening 244, and therefore, can have an increased surface area. Theincreased surface area of the silicide layer 248 can reduce theresistance between the epitaxial source/drain region 292 and the contactformed in the expanded opening 244.

The conductive material 246 includes a neck portion 246 n formed throughthe second ILD 230, the first ILD 297, the CESL 296, and a portion ofthe epitaxial source/drain region 292, and an end portion 246 e formedin the epitaxial source/drain region 292. The neck portion 246 n may bea trench or a cylinder having substantially vertical walls. The neckportion 246 n may have a width in a range from about 10 nm to about 50nm. The end portion 246 e may have an elliptical cross section areaalong the cross-section A-A (refer to FIG. 1). The end portion 246 e mayhave an ellipsoidal shape with an ellipsoidal surface facing thesilicide layer 248.

A height 246 eh of the end portion 246 e may be in a range from about 2nm to about 20 nm. A width 246 w of the end portion 246 e may be in arange from about 10 nm to about 50 nm. In some embodiments, the width246 w of the end portion 246 e may be greater than the width of the neckportion 246 n by an amount in a range from about 2 nm to about 20 nm.The depth and width of the end portion 246 e can enable increasedcontact surface of the end portion 246 e to the epitaxial source/drainregion 292, and thus, can reduce resistance therebetween.

The combination of anisotropic etch and isotropic etch described herecan expose an increased surface area of the source/drain region, andthus a contact area between the source/drain region and the contactfeature can be increased. The increased contact area can reduceresistance between the contact feature and the source/drain region, andtherefore, performance of the devices can be improved.

In an embodiment, a structure is provided. The structure includes anactive area including a source/drain region, a dielectric layer over theactive area, and a conductive feature through the dielectric layer toand contacting the source/drain region. The conductive feature includesa neck portion through the dielectric layer, and an end portionextending in the source/drain region. A width of the end portion isgreater than a width of the neck portion.

In another embodiment, a method is provided. The method includes forminga vertical opening through a dielectric layer over a source/drain regionof an active area to expose a portion of an upper surface of thesource/drain region, and expanding the vertical opening to form anexpanded opening in the dielectric layer and in the source/drain region.The expanded opening includes a neck portion through the dielectriclayer and an end portion in the source/drain region. The neck portionhas a first width, and the end portion has a second width that isgreater than the first width.

In yet another embodiment, a method for semiconductor processing isprovided. The method includes forming a source/drain region in an activearea on a substrate, forming a dielectric layer over the active area andthe source/drain region, anisotropically etching through the dielectriclayer to form an opening, the opening exposing at least a portion of anupper surface of the source/drain region, isotropically etching, throughthe opening, the source/drain region to laterally and vertically expandan end portion of the opening, and forming a conductive feature in theopening.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure comprising: an activearea including a source/drain region, the active area being adjacent agate electrode; a dielectric layer over the active area; and aconductive feature extending through the dielectric layer and contactingthe source/drain region, wherein the conductive feature includes: a neckportion through the dielectric layer; and an end portion extending inthe source/drain region, wherein a width of the end portion is greaterthan a width of the neck portion, wherein a widest width of the endportion is at an upper surface of the source/drain region in across-sectional view parallel to a longitudinal axis of the gateelectrode.
 2. The structure of claim 1, wherein the width of the endportion is in a range from 5% to 50% more than the width of the neckportion.
 3. The structure of claim 1, wherein the end portion extends inthe source/drain region a depth in a range from 5% to 50% of a height ofthe source/drain region.
 4. The structure of claim 3, wherein the depthis in a range from 10% to 50% of the height of the source/drain region.5. The structure of claim 1, wherein the end portion has apartial-circular cross-section profile.
 6. The structure of claim 1,wherein the end portion has an elliptical cross-section profile.
 7. Thestructure of claim 1 further comprising a silicide layer disposedbetween the conductive feature and the source/drain region, wherein thesilicide layer has a partial spheroid profile or an ellipsoid profile.8. The structure of claim 1, wherein the dielectric layer comprises anetch stop layer over the active area and an interlayer dielectric layerover the etch stop layer.
 9. A semiconductor structure comprising: afirst source/drain region and a second source/drain region in an activearea on a substrate; one or more dielectric layers over the firstsource/drain region; and a conductive feature extending through the oneor more dielectric layers, the conductive feature extending below anuppermost surface of the first source/drain region in a cross-sectionalview perpendicular to a current flow direction between the firstsource/drain region and the second source/drain region, the conductivefeature having a neck portion extending through the one or moredielectric layers and an end portion extending into the firstsource/drain region, wherein a widest dimension of the end portion is atthe uppermost surface of the first source/drain region, wherein thewidest dimension of the end portion is greater than a width of the neckportion at the uppermost surface of the first source/drain region. 10.The structure of claim 9, wherein a distance from an uppermost surfaceof the source/drain region to a lowermost surface of the conductivefeature is from about 5 nm to about 20 nm.
 11. The structure of claim10, wherein the source/drain region is an epitaxial layer, the epitaxiallayer being a different semiconductor material than the substrate,wherein the distance is 10% to about 50% of a thickness of the epitaxiallayer.
 12. The structure of claim 9, wherein the widest dimension is ina range from about 14 nm to about 40 nm.
 13. The structure of claim 9,wherein the source/drain region extends over a portion of the conductivefeature.
 14. A semiconductor structure comprising: a semiconductorsubstrate, the semiconductor substrate comprising a first semiconductormaterial; an epitaxial region on the semiconductor substrate, theepitaxial region comprising a second semiconductor material; one or morea dielectric layers over the epitaxial region; and a conductive featureextending through the one or more dielectric layers, the conductivefeature comprising a first portion and a second portion, the firstportion being above an interface between the one or more dielectriclayers and the epitaxial region, the second portion being below theinterface, the first portion having the one or more dielectric layersalong opposing sidewalls, the first portion having a first width at theinterface between the one or more dielectric layers and the epitaxialregion, the second portion having the epitaxial region along opposingsidewalls, a second width of the second portion being a widest width ofthe second portion, the second width being measured at the interface,the second width being greater than the first width, the conductivefeature extending along a lower surface of the one or more dielectriclayers.
 15. The structure of claim 14, wherein the first width is in arange from about 10 nm to about 40 nm.
 16. The structure of claim 14,wherein the second width is 2 nm to 10 nm greater than the first width.17. The structure of claim 14 further comprising a silicide regioninterposed between the conductive feature and the epitaxial region. 18.The structure of claim 17, wherein the conductive feature comprises abarrier layer and a conductive fill.
 19. The structure of claim 18,wherein a thickness of the barrier layer is 2 nm or less.
 20. Thestructure of claim 18, wherein the conductive feature extends into theepitaxial region to a depth 10% to about 50% of a thickness of theepitaxial region.